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Torque Conversion Formulas

Torque is a standard term that is comprised of “distance and force”. Since the force is applied to a threaded component in a circular motion, the distance applies to the radius (center of the torque wrench drive to a designated point on the torque wrench handle). In the case of wire harness applications, it is usually expressed in INCH-POUNDS, NEWTON-METERS, or KILOGRAM-CENTIMETERS. When extensions such as a crowfoot, or strap wrench is added to a torque wrench, it changes the distance (radius), so a mathematical formula is used to determine the correct torque readings on the torque wrench to compensate for the added length. We have included the following formulas for your convenience.

When an adapter or extension is used on a torque wrench it increases the torque range of the wrench. The formulae for computing torque when using an adapter or extension
is explained below.

A = (Length) Distance from center of torque wrench square drive to center of the puller’s hand grip.

B = Distance from center of torque wrench square drive to center of drive at end of extension.

C = (Torque) Torque wrench setting.

D = Torque desired at drive on end of extension.

P = (Force) Pull applied.

To determine torque wrench setting: C = (D*A) / (A+B)

NOTE: After computing “C” and setting wrench to computation, measure and mark “A” where pull is applied.

It is recommended that the axis of the extension always be used in line with axis of the torque wrench as shown above.

Should it be necessary, due to obstructions, to have an angle between the two axes, then the above formula is modified as follows. Due to increasing rounding errors, keep the angle as small as possible.

A, B, C, D, & P are the same as above.

E = Effective moment arm of the extension.

Ø = Angle between extension axis and torque wrench axis.

E = (B)(COS Ø)

Therefore:

C = (D*A) / (A+(B*COS Ø))

When Ø= 0, COS Ø= 1, then equation is reduced to C = (D*A) / (A+B)

When Ø= 90°, COS Ø = 0 then C = D (Regardless of the length B)

TORQUE CONVERSION CHARTS

These torque conversion charts were calculated for the BT-ST-301D Digital Torque Tool. If any other torque tool or instrument is used, calculate the torque conversion by using the mathematical formula above.

TORQUE CONVERSION CHART

FOR BT-BS-611 and BT-BS-618 SERIES
USED WITH BT-ST-301D

Diameter of
Part Being
Tightened

DESIRED TORQUE VALUE (in-lbs) (“D”)

40

60

80

100

120

140

160

180

200

1.00"

31

46

61

76

92

107

122

137

153

1.50"

30

45

59

74

89

104

119

134

148

1.75"

29

44

59

73

88

103

117

132

147

2.00"

29

43

58

72

87

101

116

130

145

2.25"

29

43

57

71

86

100

114

129

143

2.50"

28

42

56

70

85

99

113

127

141

2.75"

28

42

56

70

84

97

111

125

139

3.00"

28

41

55

69

83

96

110

124

138

3.25"

27

41

54

68

82

95

109

122

136

3.50"

27

40

54

67

81

94

107

121

134

3.75"

27

40

53

66

80

93

106

119

133

4.00"

26

39

52

66

79

92

105

118

131

TORQUE READING ON INSTRUMENT (“C”)

TORQUE CONVERSION CHART

FOR BT-BS-609 SERIES USED WITH BT-ST-301D

Diameter of
Part Being
Tightened

DESIRED TORQUE VALUE (in-lbs) (“D”)

40

60

80

100

120

140

160

180

200

0.50"

34

50

67

84

101

118

135

151

168

0.75"

33

50

66

83

99

116

133

149

166

1.00"

33

49

65

82

98

114

131

147

163

1.50"

32

48

64

79

95

111

127

143

159

1.75"

31

47

63

78

94

110

125

141

157

2.00"

31

46

62

77

93

108

124

139

155

2.25"

31

46

61

76

92

107

122

137

153

2.50"

30

45

60

75

90

105

121

136

151

TORQUE READING ON INSTRUMENT (“C”)

TORQUE CONVERSION CHART

FOR BT-BS-610 SERIES USED WITH BT-ST-301D

Diameter of
Part Being
Tightened

DESIRED TORQUE VALUE (in-lbs) (“D”)

40

60

80

100

120

140

160

180

200

0.25"

36

54

72

89

107

125

143

161

179

0.50"

35

52

70

87

104

122

139

156

174

0.75"

34

51

68

86

103

120

137

154

171

1.00"

34

51

67

84

101

118

135

152

169

1.50"

33

49

65

81

98

114

130

146

163

TORQUE READING ON INSTRUMENT (“C”)

FOR OUR OLDER TORQUE WRENCHES

TORQUE CONVERSION CHART

For BT-BS-609 and 610 Series used with BT-ST-751 & BT-ST-701 (older models)

Diameter of
Part BeingTightened

DESIRED TORQUE VALUE (in-lbs) (“D”)

40

60

80

100

120

140

160

180

200

.50

36

53

70

88

105

-

-

-

-

.75

35

52

69

87

104

122

-

-

-

1.00

34

51

68

85

102

120

135

-

-

1.50

33

50

67

83

100

117

133

150

-

1.75

33

49

66

82

99

115

132

148

164

2.00

33

49

65

81

97

114

130

146

162

2.25

32

48

65

80

96

112

128

144

160

2.50

32

48

62

79

95

111

127

143

158

TORQUE READING ON INSTRUMENT (“C”)

TORQUE CONVERSION CHART

For BT-BS-611 and 618 Series used with BT-ST-751 & BT-ST-701 (older models)

Diameter of
Part Being
Tightened

DESIRED TORQUE VALUE (in-lbs) (“D”)

40

60

80

100

120

140

160

180

200

.50

33

49

65

82

99

-

-

-

-

.75

32

48

64

81

97

113

-

-

-

1.00

32

48

64

80

96

112

128

-

-

1.50

31

47

62

78

93

109

125

140

-

1.75

31

46

62

77

92

108

123

139

154

2.00

30

46

61

76

91

107

122

137

152

2.25

30

45

60

75

90

105

120

135

150

2.50

30

45

59

74

89

104

119

134

149

2.75

29

44

59

74

88

103

118

132

147

3.00

29

44

58

73

87

102

116

131

145

3.25

29

43

58

72

86

101

115

129

143

3.50

28

43

57

71

85

100

114

128

142

3.75

28

42

56

70

84

99

113

127

140

4.00

28

42

56

70

84

98

111

125

139

TORQUE READING ON INSTRUMENT (“C”)

THESE FACTORS ARE CALCULATED USING A MATHEMATICAL FORMULA. SEVERAL VARIABLES INFLUENCE THE ACTUAL VALUE AND THE FACTORS ARE PUBLISHED AS A GUIDE ONLY.